Photomask, exposure control method and method of manufacturing a semiconductor device

ABSTRACT

A photomask transferring a light shield film pattern formed on a transparent substrate by a projection exposure apparatus, comprising a circuit pattern for transferring a predetermined pattern to a resist film, and an exposure monitor mark, the exposure monitor mark being formed in a manner that blocks having a predetermined width p, which are not resolved by the projection exposure apparatus, are intermittently or continuously arrayed along one direction, light shield and transmission portions are arrayed along one direction in each of the blocks, the blocks are arrayed so that a dimension ratio of the light shield and transmission portions of the blocks simply changes and the phase difference of exposure light passing through adjacent light transmission portions is approximately 180°.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2003-182452, filed Jun. 26,2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor lithography technique.In particular, the present invention relates to an exposure monitor maskfor highly accurately monitoring an effective exposure value to obtainthe maximum exposure margin. Further, the present invention relates toan exposure control method, and a method of manufacturing asemiconductor device using the foregoing exposure monitor mask.

2. Description of the Related Art

Short wavelength of exposure wavelength and high NA of projection lenshave been required with the scale down of patterns, and simultaneously,the process improvement has been made. However, the requirements of thescale down of device patterns are becoming recently stricter. It isdifficult to sufficiently obtain a degree of freedom of exposure and anexposure margin of the depth of focus; as a result, the yield isreduced. In order to effectively use less exposure margin to prevent thereduction of the yield, it is required to high-accurately controlexposure and focus.

The exposure control method is usually determined by measuring a linewidth of pattern. However, the pattern line width varies depending onnot only exposure but also focus. The scale down of patterns furtheradvances, and thereby, focus error largely affects the pattern linewidth. For this reason, it is difficult to determine whether thevariation of the pattern line width result from variations of properexposure value or focus position. Thus, the method of high accuratelycontrolling the exposure is required.

Contrary, Starikov discloses the method of measuring an effectiveexposure receiving no influence by focus variations (Alexander Starikov,SPIE Vol. 1261 Integrated Circuit Metrology, Inspection, and ProcessControl IV (1990) p. 315). Starikov proposes a mask pattern for theexposure monitor mark such that the focus error gives no influence tothe line width. According to the Starikov proposal, a block having awidth in which a pattern is not resolved in the using projectionexposure apparatus (aligner) is used. The block is arranged tocontinuously vary a dimension ratio (duty ratio) of light transmissionand shield portions of the pattern. By doing so, a mark having anirradiation gradient distribution, which does not depend on a focusstate, is formed on a wafer. In other words, only zero-order diffractedlight passing the vicinity of the center of the lens within the NA isfocused in a diffracted light image of the mask pattern for the exposuremonitor mark. By doing so, effective exposure is monitored withoutreceiving the influence by defocus.

The scale down further advances, and in addition, a process of using analternating phase shift mask increases. For this reason, when the maskpattern for the exposure monitor mark is formed in the alternating phaseshift mask, there are new problems, which do not so far arise in normalbinary mask or half-tone phase shift mask.

When the normal binary mask or half-tone phase shift mask is used,diffracted light is generated from mask pattern corresponding to devicepattern to be monitored on the mask. In the diffracted light, zero-orderand and ± first-order diffracted light contributes to image formation(imaging) on the wafer. The diffracted light strength has a relation ofzero order ≧± first order. The ± first-order diffracted light hasshading portions at the edge portion of pupil. For this reason, thezero-order diffracted light largely contributes as exposure. Theexposure monitor mark is formed by the mask pattern for the exposuremonitor mark in which only zero-order diffracted light is projected onthe wafer. Thus, the dimension of the exposure monitor mark is measuredto calculate variations of the effective exposure. From the calculatedvariations, the variations described below are high accuratelymonitored. One is an exposure apparatus dose variation. Another is postexposure bake (PEB) temperature variation and PEB time variation.Another is a resist sensitivity variation. Another is an effectiveexposure variation by the change of resist or front-end film thicknessresulting from standing wave effect.

However, in the alternating phase shift mask, no zero-order diffractedlight of the lens of actual device mask pattern is generated due toalternating phase shift effect. The foregoing ± first-order diffractedlight forms a latent image of the actual device pattern. A conventionalexposure monitor mark is formed by only zero-order diffracted lightpassing the vicinity of the center of the projection lens. The incidentangle onto the resist film is different between diffracted light forforming the latent image of the exposure monitor mark and the latentimage of the actual device pattern.

As a result, if the effective exposure variation is monitored using theexposure mask mark, it is possible to monitor variations resulting fromof the foregoing exposure apparatus dose, PEB temperature and PEB time.However, in the variation resulting from the foregoing resist orfront-end film thickness variation, the incident angle onto the resistis largely different in formation between the mask pattern for theexposure monitor mark and actual pattern. For this reason, the influenceby standing wave effect is different; therefore, the effective exposurewith respect to the actual pattern is not monitored highly accurately.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amask including a transparent substrate transparent to exposure light anda light shield film formed on the transparent substrate, and formed withan exposure monitor mark for monitoring exposure when transferring acircuit pattern on the mask to a resist formed on a wafer by aprojection exposure apparatus, the exposure monitor mark being formed ina manner that blocks having a predetermined width p, which are notresolved by the projection exposure apparatus, are intermittently orcontinuously arrayed along one direction, light shield and transmissionportions are arrayed along one direction in each of the blocks, theblocks are arrayed so that a dimension ratio of the light shield andtransmission portions of the blocks simply changes and a phasedifference of exposure light passing through adjacent light transmissionportions is approximately 180°.

According to one aspect of the present invention, there is provided anexposure control method comprising: preparing a projection exposureapparatus; preparing a photomask which including a transparentsubstrate, and a light shield film which having patterns to betransferred to a resist film formed on a wafer by the projectionexposure apparatus formed on the transparent substrate, the patternsincluding, a mask pattern for the target pattern to form a latent imagepredetermined pattern to the resist film, and a mask pattern for theexposure monitor mark to form an exposure monitor mark whose dimensionchanges in accordance with exposure to the resist film, the mask patternfor the exposure monitor mark being formed in a manner that blockshaving a predetermined width p, which are not resolved by the projectionexposure apparatus, are intermittently or continuously arrayed along onedirection, light shield and transmission portions are arrayed along onedirection in each of the blocks, the blocks are arrayed so that adimension ratio of the light shield and transmission portions of theblocks simply changes and a phase difference of exposure light passingthrough adjacent light transmission portions is approximately 180°;transferring the mask pattern for the exposure monitor mark to theresist film using the projection exposure apparatus to form a latentimage of the exposure monitor mark on the resist film; measuring adimension of an exposure monitor mark obtained by developing the latentimage of the exposure monitor mark and/or the resist film; calculating adifference between an optimum exposure value when transferring thepattern formed on the photomask to the resist film and an predeterminedexposure value preset in the projection exposure apparatus based on themeasurement result; and changing the predetermined exposure value inaccordance with the calculated difference.

According to one aspect of the present invention, there is provided amethod of manufacturing a semiconductor device, comprising: preparing aprojection exposure apparatus; preparing a photomask which including atransparent substrate and, and a light shield film which having patternsto be transferred to a resist film formed on a wafer by the projectionexposure apparatus formed on the transparent substrate, the patternsincluding, a mask pattern for circuit pattern to form a latent image ofa predetermined circuit pattern to a resist film; and a mask pattern forthe exposure monitor mark to form a latent image of an exposure monitormark whose dimension changes in accordance with exposure to the resistfilm, the mask pattern for the exposure monitor mark being formed in amanner that blocks having a predetermined width p, which are notresolved by the projection exposure apparatus, are intermittently orcontinuously arrayed along one direction, light shield and transmissionportions are arrayed along one direction in each of the blocks, theblocks are arrayed so that a dimension ratio of the light shield andtransmission portions of the blocks simply changes and a phasedifference of exposure light passing through adjacent light transmissionportions is approximately 180°; transferring the mask pattern for theexposure monitor mark to the resist film using the projection exposureapparatus to form a latent image of the exposure monitor mark on theresist film; measuring a dimension of an exposure monitor mark obtainedby developing the latent image of the exposure monitor mark and/or theresist film; calculating a difference between an optimum exposure valuewhen transferring the pattern formed on the photomask to the resist filmand an predetermined exposure value preset in the projection exposureapparatus based on the measurement result; and changing at least one ofexposure of the projection exposure apparatus, heat treatment time in aheat process after exposure, heat treatment temperature in the heatprocess, development time in a development process, developertemperature or developer concentration in accordance with the calculateddifference.

According to one aspect of the present invention, there is provided amethod of manufacturing a semiconductor device, comprising: preparing aprojection exposure apparatus; preparing a photomask which including atransparent substrate and, and a light shield film which having patternsto be transferred to a resist film formed on a wafer by the projectionexposure apparatus formed on the transparent substrate, the patternsincluding, a mask pattern for circuit pattern to form a latent image ofa predetermined circuit pattern to a resist film; and first and secondmask patterns for the exposure monitor mark to form each latent image ofexposure monitor mark whose dimension changes in accordance withexposure to the resist film, the first mask pattern for the exposuremonitor mark being formed in a manner that first blocks having apredetermined width p, which are not resolved by the projection exposureapparatus, are intermittently or continuously arrayed along onedirection, first light shield and transmission portions are arrayedalong one direction in each of the first blocks, the first blocks arearrayed so that a dimension ratio of the first light shield andtransmission portions of the first blocks simply changes and a phasedifference of exposure light passing through adjacent first lighttransmission portions is approximately 180°, the second mask pattern forthe exposure monitor mark being formed in a manner that second blockshaving a predetermined width p, which are not resolved by the projectionexposure apparatus, are intermittently or continuously arrayed along onedirection, second light shield and transmission portions are arrayedalong one direction in each of the second blocks, the second blocks arearrayed so that a dimension ratio of the second light shield andtransmission portions of the second blocks simply changes and a phasedifference of exposure light passing through adjacent second lighttransmission portions is approximately 0°; transferring the first andsecond mask patterns for the exposure monitor mark to the resist filmusing the projection exposure apparatus to form each latent image of thefirst and second exposure monitor marks on the resist film; measuringeach dimension of the first and second exposure monitor marks obtainedby developing the latent image of the first and second exposure monitormark and/or the resist film; calculating a first effective exposurebased on the dimension of the first exposure monitor mark; calculating asecond effective exposure based on the dimension of the second exposuremonitor mark; and changing at least one of deposit condition of afront-end formed under the resist film or resist film coating conditionif the first and second effective exposure have a relation differentfrom each other.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a top plan view schematically showing a mask pattern for theexposure monitor mark according to a first embodiment of the presentinvention;

FIG. 2 is a cross-sectional view to explain the structure of a maskpattern for the exposure monitor mark according to the first embodiment;

FIG. 3 is a view showing the pupil plane distribution of a diffractedlight passing through the mask pattern for the exposure monitor markaccording to the first embodiment;

FIG. 4 is a cross-sectional view to explain the structure of a photomaskaccording to the first embodiment;

FIG. 5 is a plan view showing the pupil plane distribution of adiffracted light of the mask pattern for the exposure monitor markaccording to the first embodiment;

FIG. 6 is a view showing a diffracted light (zero-order diffractedlight) passing through the mask pattern for the exposure monitor markaccording to the first embodiment;

FIG. 7 is a view to explain a conventional mask pattern for the exposuremonitor mark;

FIG. 8 is a view showing the pupil plane distribution of a diffractedlight image (zero-order diffracted light) of a binary mask pattern forthe exposure monitor mark;

FIG. 9 is a view showing a diffracted light (zero-order diffractedlight) of the conventional mask pattern for the exposure monitor mark;

FIG. 10 is a characteristic chart to explain resist film thicknessdependency of absorption dose of the exposure monitor mark according tothe first embodiment and a target pattern;

FIG. 11 is a characteristic chart to explain resist film thicknessdependency of absorption dose of the conventional exposure monitor markand a target pattern;

FIG. 12 is a view to explain the difference between the exposure controlusing the conventional mask pattern for the exposure monitor mark andthe exposure control using a phase shift mask pattern for the exposuremonitor mark;

FIG. 13 is a flowchart to explain the process of manufacturing asemiconductor device according to the first embodiment;

FIG. 14 is a cross-sectional view to explain the structure of aphotomask according to a second first embodiment of the presentinvention;

FIG. 15 is a view showing diffracted light images passing through a maskpattern for the exposure monitor mark and a 460-nm pitch phase shifttarget pattern according to the second embodiment;

FIG. 16 is a view showing diffracted light of the mask pattern for theexposure monitor mark and the 460-nm pitch phase shift target pattern;

FIG. 17 is a characteristic chart to explain resist film thicknessdependency of absorption dose of the exposure monitor mark and the460-nm pitch target pattern;

FIG. 18 is a view to explain resist film thickness variation dependencyof two target pattern dimensions and resist film thickness variationdependency of effective exposure detected by two exposure monitor marks;

FIG. 19 is a flowchart to explain the process of manufacturing asemiconductor device according to the second embodiment; and

FIG. 20 is a cross-sectional view to explain the structure of the maskpattern for the exposure monitor mark according to the secondembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings.

(First Embodiment)

The first embodiment for solving the foregoing problem will be explainedbelow.

The inventors have formed a conventional mask pattern for the exposuremonitor mask in an alternating phase shift mask. In this case, it isimpossible to monitor an effective exposure variation relevant tothickness variation of under-layer or resist film. For this reason,highly accurate critical dimension (CD) control is not achieved. Thefollowing method is given in order to solve the problem described above.

An ArF excimer laser projection exposure apparatus was used. In theprojection exposure apparatus, the exposure wavelength λ is 193 nm, thenumerical aperture NA on the wafer is 0.68, and the coherence factor σis 0.34. The projection exposure apparatus is provided with analternating photomask. The pattern formed on the alternating photomaskis transferred to a positive resist film on a wafer. The details of thepattern at unnecessary edge portions peculiar to the alternatingphotomask are omitted here. In brief, the pattern at unnecessary edgeportions is removed by carrying out double exposure after the pattern istransferred. The following is an explanation about an example applied tothe case of forming a resist-remaining pattern having a pitch of 190 nmand a width of 80 nm as the dimension of a resist pattern (targetpattern) formed on the wafer.

FIG. 1 is a top plan view schematically showing a mask pattern for theexposure monitor mark according to a first embodiment of the presentinvention. FIG. 2 is a cross-sectional view to explain the structure ofthe mask pattern for the exposure monitor mark shown in FIG. 1.

As shown in FIG. 1 and FIG. 2, a mask pattern 100 for the exposuremonitor mark is formed in a manner that a block having a width p iscontinuously arrayed. The block includes light transmission portions101, 102 and a light shield portion 103. The selected width p is adimension, which is not resolved by the used exposure apparatus(aligner). The foregoing light transmission portions 101, 102 and lightshield portion 103 are arrayed along the arrangement direction of theblock. The duty ratio of each block is set so that the duty ratio of thelight transmission portions 101, 102 and the light shield portion 103included in each arrayed block simply changes. Incidentally, severalblocks may be intermittently arrayed.

In FIG. 2, a reference numeral 110 denotes a transparent substrate suchas silica (quartz) glass, 111 denotes a light shield film, and 112denotes a phase shifter (optical film). The thickness of the phaseshifter 112 is adjusted as follows. Light transmitted through thetransparent substrate 110 is shifted by an angle of 180° with respect tothe phase of light transmitted through the transparent substrate 110without transmitting through the phase shifter 112. As illustrated inFIG. 2, the light transmission portion 101 is not formed with the phaseshifter 112. On the other hand, the light transmission portion 102 isformed with the phase shifter 112.

When illumination light is irradiated on to the mask pattern for theexposure monitor mark, the following characteristic appears. That is,the intensity distribution of a diffracted light of the mask pattern forthe exposure monitor mark on the substrate surface simply decreases orincreases without depending on the focus position.

As described above, the phase of each light transmitted through adjacentlight transmission portions is shifted by an angle of 180°. The phaseshift mask pattern for the exposure monitor mark is used, and thereby,an exposure monitor mark is formed on the wafer surface. In this case,the zero-order diffracted light generated from the mask pattern for theexposure monitor mark is not projected on the resist film, like the maskpattern for the target pattern requiring dimension control in actual. Inaddition, the exposure monitor mark dose not depend on focus by ±first-order diffracted light.

As seen from the diffracted light image on the pupil plane shown in FIG.3, the preferable condition described below is given. The condition isobtain a diffraction angle wider than a state that the center of a ±first-order diffracted light 202 overlaps the edge of a pupil plane 201of a projection optical system of the exposure apparatus. Thus, thecondition of the width p of the block, which is not resolved by theexposure apparatus, does not depend on the coherence factor σ. In orderto prevent the block from being resolved by the exposure apparatus, thefollowing requirement is set. More specifically, when an exposuremonitor pattern is projected on to the resist film using the projectionexposure apparatus, the width of the array direction of a projectionimage corresponding to the block is set as P. The width P is expressedby the following equation (1).P≦λ/2NA  (1)

In the mask pattern 100 for the exposure monitor mark, the width P isset to 140 nm to satisfy the foregoing equation (1).

The phase shift mask pattern for the exposure monitor mark designed inthe foregoing manner is used. In this way, diffracted light images ofthe mask patterns for the target pattern and for the exposure monitormark are formed at the position near to each other on the pupil plan ofthe projection optical system. Thus, the diffracted light image of themask pattern for the exposure monitor mark reduces the influence bystanding wave effect in which the diffracted light image of the maskpatterns for the target pattern receives from thickness variation of thefront-end film. The effect of the mask pattern for the exposure monitormark will be explained below comparing with a conventional mask patternfor the exposure monitor mark.

In FIG. 4 to FIG. 6, there are shown a mask pattern for the exposuremonitor mark (width P=140 nm) according to the first embodiment and analternating mask pattern for the target pattern having a pitch of 190nm. That is, there are shown diffracted light images of the foregoingtwo mask patterns on the pupil plane of the projection optical systemand incident states on the wafer surface. FIG. 4 is a cross-sectionalview schematically showing the structure of a photomask. In FIG. 4, areference numeral 300 denotes a transparent substrate, and 302 denotes amask pattern for the target pattern.

In FIG. 5, there is shown a diffracted light image (± first-orderdiffracted light) 311 on the pupil plane 201 of the mask pattern 100 forthe exposure monitor mark of the present embodiment. As depicted in FIG.5, the diffracted light image 311 of the alternating mask pattern 100for the exposure monitor mark of the embodiment and a diffracted lightimage 312 of the mask pattern 302 for the target pattern are projected.In this case, the foregoing two diffracted light images 311 and 312 areprojected at nearly the same position on the pupil plane 201. FIG. 6 isa view to explain the incident angle on the wafer surface betweendiffracted light of the alternating mask pattern for the exposuremonitor mark and the mask pattern for the target pattern. As seen fromFIG. 6, the incident angle of the diffracted light 321 of thealternating mask pattern 100 for the exposure monitor mark isapproximately the same as the diffracted light 322 of the mask pattern302 for the target pattern.

Contrary, FIG. 7 shows a conventional binary mask pattern 400 for theexposure monitor mark. In FIG. 7, a reference numeral 401 denotes alight transmission portion, and 403 denotes a light shield portion. InFIG. 8, there is shown each position on the pupil plane of diffractedlight images of mask patterns for the exposure monitor mark and targetpattern. As illustrated in FIG. 8, a diffracted light image (zero-orderlight image) 315 of the binary mask pattern 400 for the exposure monitormark and the diffracted light image 312 of the mask pattern 302 for thetarget pattern are projected. In this case, the foregoing two diffractedlight images 315 and 312 are projected at the position different fromeach other on the pupil plane 201.

The binary mask pattern 400 for the exposure monitor mark is formed in amanner that a block having a predetermined width incapable of beingresolved by the used exposure apparatus is continuously arrayed. In eachblock, light transmission and shield portions are arrayed along thearrangement direction of the block. The duty ratio of each block is setso that the duty ratio of light transmission and shield portions arrayedin each block simply changes. Incidentally, several blocks may beintermittently arrayed. The condition for preventing the block frombeing resolved by the exposure apparatus is expressed by the followingequation.λ/P′≧(1+σ)NA

Where, P′ is a width of the arrangement direction of the projected imagecorresponding to the block when exposure monitor pattern is projected onthe resist film using the projection exposure apparatus.

FIG. 9 is a view to explain the incident angle on the wafer surfacebetween a diffracted light 325 of the binary mask pattern for theexposure monitor mark and a diffracted light 322 of the mask pattern forthe target pattern. In FIG. 9, a reference numeral 331 denotes a wafer,and 332 denotes a resist film. As seen from FIG. 9, the incident angleof the diffracted light 325 of the binary mask pattern 400 for theexposure monitor mark is quite different from the diffracted light 322of the mask pattern 302 for the target pattern.

FIG. 10 is a characteristic chart to explain absorption dose withrespect to the resist film in the phase shift mask pattern for theexposure monitor mark and the mask pattern for the target pattern. FIG.11 is a characteristic chart to explain absorption dose with respect tothe resist film in the binary mask pattern for the exposure monitor markand the mask pattern for the target pattern. A resist film, oxide film(110 nm), organic anti-reflection film (300 nm) and Si are used as thefront-end film. Judging from the result, the absorption dosecharacteristic with respect to resist is the same in the phase shiftmask pattern for the exposure monitor mark and the mask pattern for thetarget pattern. Therefore, it is possible to accurately detect (ormonitor) effective exposure variation with respect to thicknessvariation of front-end and resist films.

FIG. 12 is a view to explain the difference between the exposure controlusing the phase shift mask pattern for the exposure monitor mark and theexposure control using the binary mask pattern for the exposure monitormark. In FIG. 12, the solid line shows the dimensional variation oftarget pattern. On the other hand, the dotted chain and the broken lineindividually show effective exposure measured using the conventionalexposure monitor mark and the exposure monitor mark of the presentinvention. Based on FIG. 12, exposure control will be detailedlyexplained below.

First, the exposure process was carried out under the condition that theinitial film thickness of resist is set to 0.22 μm. At that time, thefilm thickness of resist varies due to any causes; as a result, thereappears dimensional variation shown by the solid line of FIG. 12. Theforegoing change is monitored using the mask pattern for the exposuremonitor mark of the present invention. In this case, as seen from thebroken line of FIG. 12, dimensional variation of the target pattern ismonitored as effective exposure variation.

Contrary, the foregoing change is monitored using the conventional maskpattern for the exposure monitor mark. In this case, if the resistbecomes thin, misjudgment is made such that the exposure should bereduced although it must be essentially increased to make small thetarget dimension. As a result, it can be seen that a pattern having adimension considerably different from the target dimension is formed.

As described above, the phase shift mask pattern for the exposuremonitor mark is used. By doing so, it is possible to acutely detect theeffective exposure variation caused by thickness variation of resist andfront-end films in alternating and phase shift mask patterns for thetarget pattern. Thus, highly accurate dimension control is achieved.

The method of manufacturing a semiconductor device using the maskpattern for the exposure monitor mark will be explained below. FIG. 13is a flowchart to explain the process of manufacturing a semiconductordevice according to the first embodiment of the present invention.

First, a resist film is formed on a wafer (step S101). A phase shiftmask pattern for the exposure monitor mark is transferred to the resistfilm to form a latent image of exposure monitor mark (step S102). Afterexposure, post exposure bake (PEB) and development are carried out toobtain an exposure monitor mark (step S103).

An inspection sample is extracted to measure the dimension of analternating exposure monitor mark (step S104). The dimension, that is,the latent image of the exposure monitor mark may be measured after thePEB, and not the development. An effective exposure is obtained from themeasured dimension (Step S105).

A variation of the effective exposure with respect to design exposure iscalculated (step S106). It is determined whether or not the variation isless than an allowable value (step S107). If the variation is less thanthe allowable value, the next process is carried out without changingthe exposure condition and the process condition after that (step S108).

If the variation is larger than the allowable value, the exposurecondition and the process condition after that are changed (step S109).

The foregoing process condition after that includes exposure settingvalues of exposure apparatus, process time in PEB process, processtemperature, development time, developer temperature or concentration.The process condition after that further includes exposure processconditions such as resist coating condition and front-end thicknesscondition. These conditions described above are changed in accordancewith the value calculated in step S106.

The present invention is not limited to the phase shift mask pattern forthe exposure monitor mark described in FIG. 1 and FIG. 2. For example,an inverted pattern of the pattern shown in FIG. 1 and FIG. 2 isapplicable. FIG. 1 and FIG. 2 show the structure in which the shifterconverting the phase by an angle of 180° is bonded. Any other forms areapplicable so long as phase shift is made so that no zero-orderdiffracted light is generated with respect to the mask pattern for theexposure monitor mark. For example, even if the mask pattern for theexposure monitor mark is formed in a manner of engraving the transparentsubstrate, the same effect is expected.

(Second Embodiment)

The first embodiment has explained about micro pattern such asalternating mask pattern for the target pattern having a 190-nm pitch.For practical use, line width accuracy is required with respect to apattern having a wider pitch.

In the second embodiment, the effective exposure relevant to thicknessvariation of a front-end film is accurately detected with respect to thefollowing two patterns. One is a pattern having a pitch of 190 nm, andanother is a pattern having a relatively large pitch of 460 nm althoughthe target dimension is the same. By doing so, highly accurate CDcontrol is achieved. The method of achieving the highly accurate CDcontrol will be described below.

In the second embodiment, the same exposure conditions as the firstembodiment are given. More specifically, an ArF excimer laser projectionexposure apparatus was used. In the projection exposure apparatus, theexposure wavelength λ is 193 nm, the numerical aperture NA on the waferis 0.68, and the coherence factor σ is 0.34. The projection exposureapparatus is provided with an alternating photomask. The pattern formedon the alternating photomask is transferred to a positive resist film ona wafer. The details of the pattern at unnecessary edge portionspeculiar to the alternating type are omitted here. In brief, the patternat unnecessary edge portions is removed by carrying out double exposureafter the pattern is transferred. The following is an explanation aboutan example of forming two resist-remaining patterns having 190-nm and460-nm pitches and a width of 80 nm as the target pattern dimension.

It is difficult to high accurately control mask patterns for the targetpattern having different pitch. This is because the influence bystanding wave effect in the foregoing two patterns is different if thethickness of the front-end film is different. For this reason, it isimportant whether process variation is detection and correction areimmediately made if process variation with respect to resist andfront-end film thickness occurs.

The present inventors have found the method given below. According tothe method, effective exposure variation including standing wave effectis monitored with respect to two patterns having 190-nm and 460-nmpitches. The front-end thickness variation is detected from the relationof effective exposure variation between both monitor patterns.

The foregoing method will be explained below with reference to FIG. 14,which is a cross-sectional view showing the structure of a photomaskaccording to the second embodiment. In the second embodiment, a binarymask pattern 400 for the exposure monitor mark is additionally providedas the exposure monitor. FIG. 14 shows the cross section of thephotomask. In FIG. 14, a reference numeral 100 denotes the phase shiftmask pattern for the exposure monitor mark described in the firstembodiment. A reference numeral 400 denotes a binary mask pattern 400for the exposure monitor mark, and 304 denotes a mask pattern for thetarget pattern having a pitch of 460 nm.

In FIG. 15, two diffracted light images are shown together. One is adiffracted light image (zero-order diffracted light) 313 on the pupilplane corresponding to the binary mask pattern 400 for the exposuremonitor mark. Another is a diffracted light image 314 corresponding tothe mask pattern 304 for the target pattern having a pitch of 460 nm. InFIG. 16, there are shown a diffracted light 323 of the binary maskpattern 400 for the exposure monitor mark and a diffracted light 324 ofthe mask pattern 304 for the target pattern (pitch: 460 nm).

As described in the first embodiment, the effective exposure of the 190nm pitch mask pattern 302 for the target pattern is accurately detectedinclusive of the front-end thickness variation using the phase shiftmask pattern 100 for the exposure monitor mark. On the other hand, thereis a tendency for the diffracted light 324 of the pattern 304 having alarge pitch of 460 nm to focus on the center of the pupil plane 201, asseen from FIG. 15. Thus, it can be seen that the diffracted light 324 isincident onto the resist at approximately the same angle as thediffracted light 323 of the binary mask pattern 400 for the exposuremonitor mark.

FIG. 17 is a characteristic chart to explain absorption dose to resistthickness in the mask pattern 400 for the exposure monitor mark and themask pattern 304 for the target pattern having a pitch of 460 nm. Aresist film, oxide film (110 nm), organic anti-reflection film (300 nm)and Si are used as the front-end, like the first embodiment. Judgingfrom the result, the absorption dose characteristic with respect toresist is substantially the same in the mask pattern 304 for the targetpattern having a pitch of 460 nm and the mask pattern 400 for theexposure monitor mark. Therefore, it is possible to accurately detect(or monitor) effective exposure variation with respect to the front-endthickness variation.

FIG. 18 shows resist thickness variation dependency relevant to twotarget pattern dimensions and resist thickness variation dependencyrelevant to effective exposures detected by two exposure monitor marks.In FIG. 18, the solid line and the two-dotted chain line show a maskpattern dimension for the target pattern having a pitch of 190 nm and atarget pattern dimension having a pitch of 190 nm, respectively. In FIG.18, the dotted line shows an effective exposure obtained from dimensionmeasurement of a phase shift exposure monitor mark. The dotted chainline shows an effective exposure obtained from dimension measurement ofa binary exposure monitor mark.

From the result shown in FIG. 17 and FIG. 18, the inventors haveinterested in the following matter. The difference of influence relevantto front-end thickness variation between two target pattern dimensionshaving different pitches is reflected in the effective exposurevariation between phase shift and conventional exposure monitor marksdescribed in the first embodiment.

The inventors have employed the method given below. More specifically,the effective exposure variation, in particular, resist and front-endthickness variations are immediately detected, and thereafter, thevariations are fed back to resist film coating process and front-endforming process. The method will be explained below with reference tothe flowchart shown in FIG. 19. First, front-end films such as oxidefilm and anti-reflection film are formed on a wafer (step S201). Aresist film is coated on the front-end film, and bake process beforeexposure is carried out so that a mask pattern for the exposure monitormark is transferred to the resist film (step S202). Post exposure bake(PEB) and development are carried out to form a pattern (step S203). Aninspection sample is extracted, and each dimension of binary andalternating exposure monitor marks is measured (step S204). Thedimension of exposure monitor mark may be measured after PEB or at thelatent image stage after exposure, and not after development. Fromexposed and measured dimension, each effective exposure is calculatedwith respect to the foregoing two exposure monitor marks (step S205). Avariation of the effective exposure to design exposure is calculated(step S206). It is determined whether or not the variation is less thanan allowable value (step S207). If the variation is less than theallowable value, it is unnecessary to change exposure condition andprocess condition after that (step S208).

However, if the variation is larger than the allowable value, it isdetermined whether or not each variation of two effective exposures isthe same tendency (step S209). If two effective exposures have the sametendency, it is predicted that the influence by the front-end thicknessis not given or little. Therefore, corrections are made with respect tosetting exposure of the exposure apparatus or PEB condition ordevelopment condition (step S210). However, if each effective exposurevariation obtained from two exposure monitor marks has the sametendency, the cause is the influence by variation of resist or front-endfilm thickness. For this reason, even if the exposure process or theprocess after exposure is changed, the sufficient effect is notobtained. The variation of resist or front-end film thickness ismeasured (step S211), and thereafter, deposit condition of these resistor front-end film is corrected in accordance with the measured variation(step S212).

As described above, two kinds of mask patterns for the exposure monitormark are used. By doing so, it is determined whether the variation ofthe obtained effective exposure results from the variation of resist andfront-end film thickness or causes other than those. Therefore, feedbackis possible with respect to front-end deposit process or resist coatingprocess. In particular, high accurate dimension control is achieved withrespect to several kinds of target patterns.

The resist thickness variation is given as the front-end variation. Thepresent invention is not limited to the resist. Effective exposurevariation is accurately monitored with respect to variation relevant toan oxide film or organic anti-reflection film as an other front-end,like the resist. Thus, highly accurate dimension control is achieved.

The phase shift mask pattern for the exposure monitor mark is notlimited to the structure shown in FIG. 1 and FIG. 2. For example, aninverted pattern of the pattern shown in FIG. 1 and FIG. 2 isapplicable. In FIG. 2, there is shown the structure in which the shifterconverting the phase by an angle of 180° is bonded. Any other forms areapplicable so long as the phase shift is made so that no zero-orderdiffracted light is generated with respect to the mask pattern for theexposure monitor mark. For example, even if the mask pattern for theexposure monitor mark is formed in a manner of engraving the transparentsubstrate, the same effect is expected. The structure disclosed in U.S.Pat. No. 6,226,074 is employed, and thereby, the following arrangementis given. As shown in FIG. 20, alternating mask patterns 501 to 504 forthe exposure monitor mark are arranged in the X-axis direction whilebinary mask patterns 511 to 514 for the exposure monitor mark arearranged in the Y-axis direction (and vice versa). In this way,effective exposure variation is detected as misalignment.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A photomask for transferring a light shield film pattern formed on atransparent substrate by a projection exposure apparatus onto a resistfilm formed on a wafer, comprising: a mask pattern for the targetpattern for transferring a predetermined pattern to a resist film; and amask pattern for the exposure monitor mark, the mask pattern for theexposure monitor mark being formed in a manner that blocks having apredetermined width p, which are not resolved by the projection exposureapparatus, are intermittently or continuously arrayed along onedirection, light shield and transmission portions are arrayed along onedirection in each of the blocks, the blocks are arrayed so that adimension ratio of the light shield and transmission portions of theblocks simply changes and a phase difference of exposure light passingthrough adjacent light transmission portions is approximately 180°. 2.The photomask according to claim 1, wherein an optical film is formed onone of adjacent light transmission portions, and the thickness of theoptical film is adjusted so that a phase difference between an exposurelight passing through one light transmission portion and an exposurelight passing through the other light transmission portion becomes 180°.3. The photomask according to claim 1, wherein the transparent substrateof one of adjacent light transmission portions is engraved, and theengraved rate of the transparent substrate is adjusted so that a phasedifference between an exposure light passing through one lighttransmission portion and an exposure light passing through the otherlight transmission portion becomes 180°.
 4. The photomask according toclaim 1, wherein when a wavelength of the exposure light of theprojection exposure apparatus is set as λ, a numerical aperture of thesubstrate side of the projection exposure apparatus is set as NA, and awidth of said one direction of a projection image corresponding to theblock in projecting the mask pattern for the exposure monitor mark ontothe resist film using the projection exposure apparatus when is set asP, the following relation is given:P≦λ/2NA.
 5. An exposure control method comprising: preparing aprojection exposure apparatus; preparing a photomask which including atransparent substrate, and a light shield film which having patterns tobe transferred to a resist film formed on a wafer by the projectionexposure apparatus formed on the transparent substrate, the patternsincluding, a mask pattern for the target pattern to form a latent imagepredetermined pattern to the resist film, and a mask pattern for theexposure monitor mark to form an exposure monitor mark whose dimensionchanges in accordance with exposure to the resist film, the mask patternfor the exposure monitor mark being formed in a manner that blockshaving a predetermined width p, which are not resolved by the projectionexposure apparatus, are intermittently or continuously arrayed along onedirection, light shield and transmission portions are arrayed along onedirection in each of the blocks, the blocks are arrayed so that adimension ratio of the light shield and transmission portions of theblocks simply changes and a phase difference of exposure light passingthrough adjacent light transmission portions is approximately 180°;transferring the mask pattern for the exposure monitor mark to theresist film using the projection exposure apparatus to form a latentimage of the exposure monitor mark on the resist film; measuring adimension of an exposure monitor mark obtained by developing the latentimage of the exposure monitor mark and/or the resist film; calculating adifference between an optimum exposure value when transferring thepattern formed on the photomask to the resist film and an predeterminedexposure value preset in the projection exposure apparatus based on themeasurement result; and changing the predetermined exposure value inaccordance with the calculated difference.
 6. The method according toclaim 5, wherein an optical film is formed on one of adjacent lighttransmission portions, and the thickness of the optical film is adjustedso that a phase difference between an exposure light passing through onelight transmission portion and an exposure light passing through theother light transmission portion becomes 180°.
 7. The method accordingto claim 5, wherein the transparent substrate of one of adjacent lighttransmission portions is engraved, and the engraved rate of thetransparent substrate is adjusted so that a phase difference between anexposure light passing through one light transmission portion and anexposure light passing through the other light transmission portionbecomes 180°.
 8. The method according to claim 5, wherein when awavelength of the exposure light of the projection exposure apparatus isset as λ, a numerical aperture of the substrate side of the projectionexposure apparatus is set as NA, and a width of said one direction of aprojection image corresponding to the block in projecting the maskpattern for the exposure monitor mark onto the resist film using theprojection exposure apparatus when is set as P, the following relationis given:P≦λ/2NA.
 9. A method of manufacturing a semiconductor device,comprising: preparing a projection exposure apparatus; preparing aphotomask which including a transparent substrate and, and a lightshield film which having patterns to be transferred to a resist filmformed on a wafer by the projection exposure apparatus formed on thetransparent substrate, the patterns including, a mask pattern forcircuit pattern to form a latent image of a predetermined circuitpattern to a resist film; and a mask pattern for the exposure monitormark to form a latent image of an exposure monitor mark whose dimensionchanges in accordance with exposure to the resist film, the mask patternfor the exposure monitor mark being formed in a manner that blockshaving a predetermined width p, which are not resolved by the projectionexposure apparatus, are intermittently or continuously arrayed along onedirection, light shield and transmission portions are arrayed along onedirection in each of the blocks, the blocks are arrayed so that adimension ratio of the light shield and transmission portions of theblocks simply changes and a phase difference of exposure light passingthrough adjacent light transmission portions is approximately 180°;transferring the mask pattern for the exposure monitor mark to theresist film using the projection exposure apparatus to form a latentimage of the exposure monitor mark on the resist film; measuring adimension of an exposure monitor mark obtained by developing the latentimage of the exposure monitor mark and/or the resist film; calculating adifference between an optimum exposure value when transferring thepattern formed on the photomask to the resist film and an predeterminedexposure value preset in the projection exposure apparatus based on themeasurement result; and changing at least one of exposure of theprojection exposure apparatus, heat treatment time in a heat processafter exposure, heat treatment temperature in the heat process,development time in a development process, developer temperature ordeveloper concentration in accordance with the calculated difference.10. The method according to claim 9, wherein an optical film is formedon one of adjacent light transmission portions, and the thickness of theoptical film is adjusted so that a phase difference between an exposurelight passing through one light transmission portion and an exposurelight passing through the other light transmission portion becomes 180°.11. The method according to claim 9, wherein the transparent substrateof one of adjacent light transmission portions is engraved, and theengraved rate of the transparent substrate is adjusted so that a phasedifference between an exposure light passing through one lighttransmission portion and an exposure light passing through the otherlight transmission portion becomes 180°.
 12. The method according toclaim 9, wherein when a wavelength of the exposure light of theprojection exposure apparatus is set as λ, a numerical aperture of thesubstrate side of the projection exposure apparatus is set as NA, and awidth of said one direction of a projection image corresponding to theblock in projecting the mask pattern for the exposure monitor mark ontothe resist film using the projection exposure apparatus when is set asP, the following relation is given:P≦λ/2NA.
 13. A method of manufacturing a semiconductor device,comprising: preparing a projection exposure apparatus; preparing aphotomask which including a transparent substrate and, and a lightshield film which having patterns to be transferred to a resist filmformed on a wafer by the projection exposure apparatus formed on thetransparent substrate, the patterns including, a mask pattern forcircuit pattern to form a latent image of a predetermined circuitpattern to a resist film; and first and second mask patterns for theexposure monitor mark to form each latent image of exposure monitor markwhose dimension changes in accordance with exposure to the resist film,the first mask pattern for the exposure monitor mark being formed in amanner that first blocks having a predetermined width p, which are notresolved by the projection exposure apparatus, are intermittently orcontinuously arrayed along one direction, first light shield andtransmission portions are arrayed along one direction in each of thefirst blocks, the first blocks are arrayed so that a dimension ratio ofthe first light shield and transmission portions of the first blockssimply changes and a phase difference of exposure light passing throughadjacent first light transmission portions is approximately 180°, thesecond mask pattern for the exposure monitor mark being formed in amanner that second blocks having a predetermined width p, which are notresolved by the projection exposure apparatus, are intermittently orcontinuously arrayed along one direction, second light shield andtransmission portions are arrayed along one direction in each of thesecond blocks, the second blocks are arrayed so that a dimension ratioof the second light shield and transmission portions of the secondblocks simply changes and a phase difference of exposure light passingthrough adjacent second light transmission portions is approximately 0°;transferring the first and second mask patterns for the exposure monitormark to the resist film using the projection exposure apparatus to formeach latent image of the first and second exposure monitor marks on theresist film; measuring each dimension of the first and second exposuremonitor marks obtained by developing the latent image of the first andsecond exposure monitor mark and/or the resist film; calculating a firsteffective exposure based on the dimension of the first exposure monitormark; calculating a second effective exposure based on the dimension ofthe second exposure monitor mark; and changing at least one of depositcondition of a front-end formed under the resist film or resist filmcoating condition if the first and second effective exposure have arelation different from each other.
 14. The method according to claim13, wherein an optical film is formed on one of adjacent lighttransmission portions, and the thickness of the optical film is adjustedso that a phase difference between an exposure light passing through onelight transmission portion and an exposure light passing through theother light transmission portion becomes 180°.
 15. The method accordingto claim 13, wherein the transparent substrate of one of adjacent lighttransmission portions is engraved, and the engraved rate of thetransparent substrate is adjusted so that a phase difference between anexposure light passing through one light transmission portion and anexposure light passing through the other light transmission portionbecomes 180°.
 16. The method according to claim 13, wherein when awavelength of the exposure light of the projection exposure apparatus isset as λ, a numerical aperture of the substrate side of the projectionexposure apparatus is set as NA, and a width of said one direction of aprojection image corresponding to the block in projecting the maskpattern for the exposure monitor mark onto the resist film using theprojection exposure apparatus when is set as P₁, the following relationis given:P ₁≦λ/2NA.